Converting an iMac to Ubuntu machine

I have a 2011 iMac that I converted to a Lubuntu machine. It works really well. Just about everything is so much faster. I’m very pleased with the results, except . . .

It has an older HD and it takes about 75 seconds to boot all the way up. Since replacing the HD on this particular iMac is very challenging, and requires removal of so many parts, I don’t think I want to replace the HD with an SSD.

Could I put the boot files and perhaps some other stuff on a fast 64G mini sd card, and keep it inserted in the computer at all times? I could still use the internal HD for file storage.

Is that likely to speed up the boot time?

I could live with the 75 second boot time, but I wonder if there’s anything I can do to cut down that time, that is not super labor intensive.

For example, I replaced the HD to an SSD on an older Lenovo laptop, and with Lubuntu, it boots in 32 seconds.

What are my best options for improving boot time on this 2011 iMac?

The support gurus in our support venues are awaiting your support question.

Unfortunately, this is not the right place for support. Sorry.